![](http://datasheet.mmic.net.cn/230000/79RC32438-200BB_datasheet_15568909/79RC32438-200BB_282.png)
IDT PCI Bus Interface
Disabled Mode
79RC32438 User Reference Manual
10 - 14
November 4, 2002
Notes
During a cold reset, the RC32438’s PCI reset output is tri-stated since it is not yet known if the RC32438
will be operating in host or satellite mode. Therefore, system designers should pull the PCI reset signal
down so that it is held low following the application of power to the system.
Disabled Mode
When the EN bit in the PCIC register is cleared, the PCI bus interface is disabled. The PCI bus interface
may be permanently disabled during boot configuration by selecting the disable PCI mode. When disabled,
the PCI bus interface enters a benign low-power mode. The values on all PCI input pins are ignored. The
PCI clock (PCICLK) should be driven to a valid logic level on the board.
When the PCI bus interface is disabled, all of the PCI pins are tri-stated and thus should be held at a
valid logic level on the board. The PCI bus interface may be disabled at any time after a cold reset by
clearing the enable (EN) bit in the PCI configuration (PCIC) register.
Disabling and then re-enabling the PCI bus interface resets all of the logic associated with the PCI bus
interface and causes all FIFOs to be reset. The states of all status registers are reset to their initial values,
but the states of all configuration registers are preserved.
PCI Host Mode
Reset and Initialization
In PCI host mode, the PCI reset pin (PCIRSTN) is an output. The PCIRSTN pin is asserted whenever
the EN bit in the PCIC register is cleared (e.g., as the result of a warm or cold reset). Software should
ensure that the PCIRSTN pin is asserted for a minimum of 1 ms after power has stabilized and 100 μs after
the PCI clock has stabilized.
After reset, the RC32438 boots from the boot device. The PCI interface is then enabled, causing the PCI
reset pin to be de-asserted (i.e., taking the PCI bus out of reset). Initially, the Target Not Ready (TNR) bit is
set in the PCIC register. This causes all PCI bus interface target transactions to be retried and allows the
RC32438 to initialize the PCI interface and configuration registers. Once the RC32438 device completes
the initialization sequence, it clears the Target Not Ready (TNR) bit, allowing PCI masters to access the
RC32438.
A warm reset may be initiated by writing to the Warm Reset (WR) bit in the PCI Management (PMGT)
register in PCI configuration space. An NMI to the CPU core may be initiated by writing to the Non-
Maskable Interrupt (NMI) bit in the PMGT register. A PCI host may use these features to reset/reboot the
RC32438 device.
The CPU core may generate a PCI reset by clearing the EN bit in the PCIC register or by initiating a
warm or cold reset. Note that system designers may choose to generate the PCI reset signal using external
logic rather than the RC32438 PCIRSTN signal to reset other external devices. In such a configuration, the
externally generated reset should be configured to generate a warm or cold reset.
Bus Arbitration
PCI arbitration mode in host mode is determined by the PCI mode selected during boot configuration.
The PCI host can be configured to use an external arbiter or internal arbiter. The function of the
PCIREQN[5:0] and PCIGNTN[5:0] signals is determined by the PCI mode selected
1
and is dependent on
whether the internal arbiter is used or an external arbiter is selected.
1.
PCIREQN[4] is an alternate function of GPIO[24], PCIREQN[5] is an alternate function of GPIO[27],
PCIGNTN[4] is an alternate function of GPIO[26], and PCIGNTN[5] is an alternate function of GPIO[28].